Custom Phono Playback Equalization

The Bugle phono stage from Hagerman Technology LLC is designed to offer a flexible and customizable equalization. Figure 1 shows the simplified circuit. Each RC filter section implements a pole-zero combination that has a frequency response of the form shown in Figure 2.


Figure 1. Simple, passive, split phono equalization.


Figure 2. Frequency response of each filter section.

The transfer function is calculated mathematically by

where the characteristic time constants are given as

Knowing this, it is a relatively straightforward procedure to calculate the required component values for a desired response. The following table is an online interactive calculator that will do the math for you. Just enter standard capacitor values and the desired frequency breakpoints (turnovers). The default values shown are for modern RIAA. Table 1 lists the parameters for many of the "older" equalization curves. If the treble turnover is specified in terms of dB cut at 10kHz, use Figure 3 to convert to turnover frequency.


Calculate Filter Values

Ca: uF
Cb: uF
Bass Pole: Hz
Bass Zero: Hz
Treble Pole: kHz Ignore
Treble Zero: kHz Ignore

Ra: k
Rb: k
Rc: k
Rd: k


Calculate Bugle Values

To get the required component values for the Bugle phono stage, you must also enter the desired gain (at 1kHz). It is recommended to keep gain between 30dB and 70dB. Table 2 lists the standard 1% resistor values.

Gain: dB


Reference Information

78 rpm Coarse Groove
TypeBass CornerBass TurnoverTreble Turnover
Decca 1503400
ffrr402506360
Westrex 200 
Blumlein50250 
BSI503533180
33 & 45 rpm MicroGroove
TypeBass CornerBass TurnoverTreble Turnover
ffrr1005003000
EMI705002500
NAB 5001600
Columbia1005001590
RIAA505002122

Table 1. Equalization parameters for popular formats


Figure 3. 10kHz dB-cut to frequency conversion.

Standard 1% Resistor Values
10.014.721.531.646.468.1
10.215.022.132.447.569.8
10.515.422.633.248.771.5
10.715.823.234.049.973.2
11.016.223.734.851.175.0
11.316.524.335.752.376.8
11.516.924.936.553.678.7
11.817.425.537.454.980.6
12.117.826.138.356.282.5
12.418.226.739.257.684.5
12.718.727.440.259.086.6
13.019.128.041.260.488.7
13.319.628.742.261.990.9
13.720.029.443.263.493.1
14.020.530.144.264.995.3
14.321.030.945.366.597.6

Table 2. Standard resistor values.